Prostate cancer (PCa) is one of the most frequently diagnosed noncutaneous cancers among men in the US and is the second most common cause of cancer deaths with more than 200,000 new cases and over 30,000 deaths each year in the United States. PCa therapeutics market is growing at an annual rate of 15-20% globally.
Androgen-deprivation therapy (ADT) is the standard of treatment for advanced PCa. Patients with advanced prostate cancer undergo ADT, either by luteinizing hormone releasing hormone (LHRH) agonists, LHRH antagonists or by bilateral orchiectomy. Despite initial response to ADT, disease progression is inevitable and the cancer emerges as castration-resistant prostate cancer (CRPC). Up to 30% of patients with prostate cancer that undergo primary treatment by radiation or surgery will develop metastatic disease within 10 years of the primary treatment. Approximately 50,000 patients a year will develop metastatic disease, which is termed metastatic CRPC (mCRPC).
Patients with CRPC have a median survival of 12-18 months. Though castration-resistant, CRPC is still dependent on the androgen receptor (AR) signaling axis for continued growth. The primary reason for CRPC re-emergence is re-activation of AR by alternate mechanisms such as 1) intracrine androgen synthesis, 2) AR splice variants (AR-SV) that lack ligand binding domain (LBD), 3) AR-LBD mutations with potential to resist AR antagonists (i.e., mutants that are not sensitive to inhibition by AR antagonists, and in some cases AR antagonists act as agonists of the AR bearing these LBD mutations); and 4) amplications of the AR gene within the tumor.
A critical barrier to progress in treating CRPC is that AR signaling inhibitors such as enzalutamide, bicalutamide, and abiraterone, acting through the LBD, fail to inhibit growth driven by the N-terminal domain (NTD)-dependent constitutively active AR-SV. Recent high-impact clinical trials with enzalutamide and abiraterone in CRPC patients demonstrated that 0% of AR-V7 (the predominant AR-SV) expressing patients responded to either of the treatments, indicating the requirement for next generation AR antagonists that target AR-SVs. In addition, a significant number of CRPC patients are becoming refractory to abiraterone or enzalutamide, emphasizing the need for next generation AR antagonists.
Current evidences demonstrate that CRPC growth is dependent on constitutively active AR including AR-SV's that lack the LBD such as AR-V7 and therefore cannot be inhibited by conventional antagonists. AR inhibition and degradation through binding to a domain that is distinct from the AR LBD provides alternate strategies to manage CRPC.
Molecules that degrade the AR prevent any inadvertent AR activation through growth factors or signaling pathways, or promiscuous ligand-dependent activation. In addition, molecules that inhibit the constitutive activation of AR-SVs are extremely important to provide extended benefit to CRPC patients.
Currently only a few chemotypes are known to degrade AR which include the SARDs ARN-509, AZD-3514, and ASC-J9. However, these molecules degrade AR indirectly at much higher concentrations than their binding coefficient and they fail to degrade the AR-SVs that have become in recent years the primary reason for resurgence of treatment-resistant CRPC.
This invention describes novel AR antagonists with unique pharmacology that strongly (high potency and efficacy) and selectively bind AR (better than known antagonists), antagonize AR, and degrade AR full length (AR-FL) and AR-SV. Selective androgen receptor degrader (SARD) compounds possess dual degradation and AR-SV inhibitory functions and hence are distinct from any available CRPC therapeutics. These novel selective androgen receptor degrader (SARD) compounds inhibit the growth of PCa cells and tumors that are dependent on AR-FL and AR-SV for proliferation.
SARDs have the potential to evolve as new therapeutics to treat CRPCs that are untreatable with any other antagonists. This unique property of degrading AR-SV has extremely important health consequences for prostate cancer. Till date only one molecule (EPI-001) is reported to bind to AR-NTD and inhibit AR function and PCa cell growth, albeit at lower affinity and inability to degrade the receptor. The SARDs reported herein also bind to AR-NTD and inhibit NTD-driven AR activity.
The positive correlation between AR and PCa and the lack of a fail-safe AR antagonist, emphasize the need for molecules that inhibit AR function through novel or alternate mechanisms and/or binding sites, and that can elicit antagonistic activities within an altered cellular environment.
Traditional antiandrogens such as bicalutamide and flutamide were approved for use in prostate cancer. Subsequent studies have demonstrated the utility of antiandrogens (e.g., flutamide, spironolactone, cyproterone acetate, finasteride and chlormadinone acetate) in androgen-dependent dermatological conditions such as androgenic alopecia (male pattern baldness), acne vulgaris, and hirsutism. Prepubertal castration prevents sebum production and androgenic alopecia but this can be reversed by use of testosterone, suggesting its androgen-dependence.
The AR gene has a polymorphism of glutamine repeats (polyQ) within exon 1 which when shortened may augment AR transactivation (i.e., hyperandrogenism). It has been found that shortened polyQ polymorphisms are more common in people with alopecia, hirsutism, and acne. Classic antiandrogens are undesirable for these purposes because they are ineffective through dermal dosing and their long-term systemic use raises the risks of untoward sexual effects such as gynecomastia and impotence. Further, similar to CPRC discussed above, inhibition of ligand-dependent AR activity alone may not be sufficient as AR can be activated by various cellular factors other than the endogeneous androgens testosterone (T) and dihydrotestosterone (DHT), such as growth factors, kinases, co-activator overexpression and/or promiscuous activation by other hormones (e.g., estrogens or glucocorticoids). Consequently, blocking the binding of T and DHT to AR with a classical antiandrogen may not be sufficient to have the desired efficacy.
An emerging concept is the topical application of a SARD to destroy the AR locally to the affected areas of the skin or other tissue without exerting any systemic antiandrogenism. For this use, a SARD that does not penetrate the skin or is rapidly metabolized would be preferable.
Supporting this approach is the observation that cutaneous wound healing has been demonstrated to be suppressed by androgens. Castration of mice accelerates cutaneous wound healing while attenuating the inflammation in the wounds. The negative correlation between androgen levels and cutaneous healing and inflammation, in part, explains another mechanism by which high levels of endogenous androgens exacerbate hyperandrogenic dermatological conditions. Further, it provides a rationale for the treatment of wounds such as diabetic ulcers or even trauma, or skin disorders with an inflammatory component such as acne or psoriasis, with a topical SARD.
Androgenic alopecia occurs in ˜50% of Caucasian males by midlife and up to 90% by 80 years old. Minoxidil (a topical vasodilator) and finasteride (a systemic 5alpha reductase type II inhibitor) are FDA approved for alopecia but require 4-12 months of treatment to produce a therapeutic effect and only arrest hair loss in most with mild to moderate hair regrowth in 30-60%. Since currently available treatments have slow and limited efficacy that varies widely between individuals, and produce unwanted sexual side effects, it is important to find a novel approach to treat androgenic alopecia and other hyperandrogenic dermatologic diseases.
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. Patients with ALS are characterized by extended AR polyglutamine repeats. Riluzole is an available drug for ALS treatment, however, only provides short-term effects. There is an urgent need for drugs that extend the survival of ALS patients. Transgenic animals of ALS were shown to survive longer upon castration and reduction in AR levels compared to castration+nandrolone (agonist) supplementation. Castration reduces the AR level, which may be the reason for extended survival.
Androgens promote uterine proliferation. Higher testosterone levels increase the risk of uterine fibroids. Treatment of uterine fibroids with SARDs would help prevent or treat uterine fibroids.
Here we describe 3-amino-propanamide SARDs that bind to LBD and an alternate binding and degradation domain (BDD; located in the NTD), antagonize AR, and degrade AR thereby blocking ligand-dependent and ligand-independent AR activities. This novel mechanism produces improved efficacy when dosed systemically (e.g., for prostate cancer) or topically (e.g., dermatological diseases). X-linked spinal-bulbar muscular atrophy (SBMA—also known as Kennedy's disease) is a muscular atrophy that arises from a defect in the androgen receptor gene on the X chromosome. Proximal limb and bulbar muscle weakness results in physical limitations including dependence on a wheelchair in some cases. The mutation results in a protracted polyglutamine tract added to the N-terminal domain of the androgen receptor (polyQ AR). Binding and activation of this lengthened polyQ AR by endogeneous androgens (testosterone and DHT) results in unfolding and nuclear translocation of the mutant androgen receptor. These steps are required for pathogenesis and result in partial loss of transactivation function (i.e., an androgen insensitivity) and a poorly understood neuromuscular degeneration. Currently there are no disease-modifying treatments but rather only symptom directed treatments. Efforts to target the polyQ AR of Kennedy's disease as the proximal mediator of toxicity by harnessing cellular machinery to promote its degradation, i.e., through the use of a SARD, hold promise for therapeutic intervention. Selective androgen receptor degraders such as those reported herein bind to and degrade a variety of androgen receptors (full length, splice variant, antiandrogen resistance mutants, and are likely to degrade polyQ AR polymorphism as well), indicating that they are promising leads for treatment of SBMA.